1. Field of the Invention
This invention relates generally to cardiac stimulator leads, and more particularly to a cardiac stimulator lead including an extendable and retractable electrode that is lubricated with a biocompatible lubricant.
2. Description of the Related Art
Conventional cardiac stimulator systems consist of a cardiac stimulator and an elongated flexible cardiac lead that is connected proximally to a header structure on the cardiac stimulator and is implanted distally at one or more sites within the heart requiring cardiac stimulation or sensing. The cardiac stimulator is normally a pacemaker, a cardioverter/defibrillator, a sensing instrument, or some combination of these devices.
At the time of implantation, the distal end of a cardiac lead is inserted through an incision in the chest and manipulated by the physician to the site requiring electrical stimulation with the aid of a flexible stylet that is removed prior to closure. At the site requiring electrical stimulation, the distal end of the lead is anchored to the endocardium by an active mechanism, such as a screw-in electrode tip, or alternatively, by a passive mechanism, such as one or more radially spaced tines that engage the endocardium. The proximal end of the lead is then connected to the cardiac stimulator and the incision is closed. The implantation route and site are usually imaged in real time by fluoroscopy to confirm proper manipulation and placement of the lead.
A conventional cardiac stimulator lead normally consists of an elongated flexible tubular, electrically insulating sleeve that is connected proximally to a connector that is adapted to couple to the header of a cardiac stimulator can. The distal end of the insulating sleeve includes some type of tip electrode. To ensure that physical contact with the desired myocardial tissue is maintained after implantation, tip electrodes for most conventional leads are anchored to myocardial tissue by a fixation mechanism of one sort or another. In some leads, a corkscrew-like member is projectable from the sleeve and penetrates the endocardium. In others, the electrode is fitted with one or more radially projecting tines that engage the normally irregular surface of the endocardium. Still others may employ both types of structures.
Some conventional active fixation leads incorporate an axially moveable member that holds or is otherwise coupled to the corkscrew. The moveable member must be moved axially relative to the insulating sleeve to deploy the corkscrew. This is normally accomplished by inserting a stylet into the lead, engaging the moveable member, and applying a thrust to the stylet.
Conventional cardiac lead insulating sleeves are typically composed of biocompatible materials with sufficient flexibility to enable the lead to readily conform to the often irregular transvenous pathway from the cardiac stimulator to the endocardium. Silicone and polyurethane are two commonly used materials. Biocompatibility and superior flexibility over polyurethane has made, and continues to make silicone a frequent choice of lead designers. Silicone presents some mechanical properties that benefit the function of many silicone lead sleeves. A silicone lead sleeve exhibits an inherent tackiness that produces an adhesive-like effect on the surfaces of other structures come into contact with the sleeve. This inherent tackiness is helpful in preventing the sliding movement of the sleeve relative to other structures that are intended to remain in a fixed position relative to the sleeve. Examples of such include the lead connector and a suture sleeve (at least at the incision is closed). However, the inherent tackiness may also impede the function of many types of conventional leads. In many conventional lead designs, it is desirable and necessary to move a member that is in contact with the silicone sleeve. For example, where the lead employs active fixation in the form of a corkscrew coupled to an axially moveable member, the member must be moved relative to the sleeve to deploy the corkscrew. If the member is direct contact with the silicone sleeve, the movement may be significantly impeded by the adhesive-like character of the silicone.
Brute force may be employed in an attempt to dislodge a sticking corkscrew member. For example, the stylet may be repeatedly pushed and pulled and/or the lead tip may be massaged by hand. However, conventional leads are minute devices so these techniques present the risk of damaging the small, delicate structures in the sleeve and corkscrew member. A radiographic marker, if present in the lead, may be damaged as well.
If a sticking corkscrew member is encountered during assembly testing, the entire lead must often be scrapped if the aforementioned manual procedures do not release the corkscrew member. If a sticking problem is encountered at the time of implantation, the implanting physician will, in most cases, discard the lead in favor of devoting time and effort to dislodging the corkscrew member.
The problem of silicone sticking transcends structures positioned inside the lead. For example, suture sleeves sometimes stick to the outer surfaces of lead sleeves and complicate the implantation procedure. The advent of epicardial implantation by trocar introducer in lieu of median sternotomy or thoracotomy also presents the potential for silicone sticking. In this type of implantation procedure the silicone lead sleeve is inserted through a tubular trocar introducer into the chest cavity. The procedure may be impeded if the silicone sleeve sticks to the inner wall of the trocar introducer.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.